Circuit substrates have an electric circuit as a constituent element, and circuit substrates containing an element such as a thin film transistor (TFT), for example, are widely utilized as components of electronic devices such as liquid crystal display devices, electroluminescent display devices, and display devices using electrophoresis.
A circuit configuration of a TFT array substrate forming a portion of a TFT driven liquid crystal display panel is described below as an example. Normally, a TFT array substrate has a pixel circuit containing a structure in which the intersections of wires in an m×n matrix composed of scan lines being m rows and signal lines being n columns are provided with TFTs as switching elements. Note that drain electrode of a TFT is electrically connected to a pixel electrode. Also, peripheral circuits such as scan driver ICs (integrated circuits) and data driver ICs are electrically connected to gate wiring and source wiring extending from each TFT.
The circuits are affected by the performance of TFTs created on the TFT substrate. That is, circuits created on a TFT substrate are affected by whether the circuit is operable, whether the circuit will scale, whether the yield will increase, and the like due to the TFTs created on the circuit substrate, because the performance of the TFTs created on the TFT substrate differ depending on the material quality thereof. In conventional circuit substrates, a-Si (amorphous silicon) is largely employed due to being able to cheaply and easily form TFTs.
Meanwhile, there is disclosed below a method of manufacturing a semiconductor device in which an oxide semiconductor layer is formed instead of an amorphous silicon semiconductor layer (see Patent Document 1, for example).